Most dialysis patients in the US are >65 years and are at increased cardiovascular risk. The prevalence of atrial fibrillation (AF) is higher in dialysis patients, but estimates vary widely (7%-27%). Further, controversy persists in defining its optimal management in this setting. AF is an important risk factor for thromboembolic events such as stroke, for which dialysis patients are already at increased risk. In the general population, oral anticoagulation with warfarin reduces this risk substantially, and its benefits have been shown to clearly outweigh an increased bleeding risk. In dialysis patients, however, the relationship between these benefits and risks is less clear. While warfarin may reduce thromboembolic events, dialysis patients are at an increased bleeding risk even in the absence of warfarin. Thus, the risk of warfarin-related hemorrhage is likely to be much higher in dialysis patients. Little is known about actual warfarin treatment patterns of dialysis patients with AF, and no trials or formal benefit-risk assessments of warfarin in these patients have been conducted. In Specific Aim 1, the prevalence of AF in a very large population of older dialysis patients with prescription drug coverage will be measured (N=12,812) and clinical and demographic characteristics associated with AF will be defined. In Specific Aim 2, the rates of warfarin treatment of AF in this population will be assessed and factors associated with its use vs. non-use will be defined. In Specific Aim 3, differences in outcomes between treated vs. untreated dialysis patients with AF will be assessed by measuring rates of thromboembolic and bleeding events in AF patients receiving warfarin, compared to similar untreated AF patients. This Aim will also be studied in a separate cohort of dialysis patients from a large national dialysis provider. Control for confounding will be performed with multivariable regression as well as propensity score methods. This feasibility study (R21) will be used to develop relevant evidence that will help inform a common treatment dilemma in dialysis patient care. Subsequently, an R01 grant submission will be developed, proposing US-wide follow-up studies to clarify these issues even further. PUBLIC HEALTH RELEVANCE: We will study a common disorder of irregular heartbeat in older patients with severe kidney failure. That condition increases the risk of stroke, which is preventable with an existing medication. Since it is not known whether this drug is also the best treatment for such patients on dialysis, our work will study this question and thus lead to better care of these patients.